NTSB Identification: ATL91LA091.
The docket is stored on NTSB microfiche number 44842.
Scheduled 14 CFR operation of USAIR
Accident occurred Saturday, May 04, 1991 in MEMPHIS, TN
Probable Cause Approval Date: 02/12/1993
Aircraft: BOEING B767-287ER, registration: N651US
Injuries: 1 Serious,11 Minor,104 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

THE FLIGHT WAS IN LEVEL CRUISE FLIGHT AT FL430. THERE WAS SIGNIFICANT LEVEL 6 THUNDERSTOM ACTIVITY IN THE IMMEDIATE VICINITY OF THE TOLSA VOR AT THE TIME OF THE ACCIDENT, AND SIGMETS HAD BEEN ISSUED TO AND RECEIVED BY THE FLIGHT CREW ADVISING OF THIS ACTIVITY. THE FLIGHT CREW STATED THAT THE ONLY WEATHER BEING DEPICTED BY THEIR ON BOARD WEATHER RADAR WAS 40 MILES FROM THEIR POSITION AT THE TIME OF THE ACCIDENT AND NOT IN THEIR FLIGHT PATH. ACCORDING TO TRANSCRIPTS OF THEIR CONVERSATION WITH AIR TRAFFIC CONTROL PERSONNEL, APPROXIMATELY FIVE MILES WEST OF THE TULSA VOR AND TWO MINUTES PRIOR TO THE ACCIDENT, THE FLIGHT CREW REQUESTED AND RECEIVED PERMISSION TO DEVIATE FROM THE ASSIGNED COURSE IN ORDER TO AVOID BUILDUPS IN THEIR FLIGHT PATH. THE FLIGHT ENCOUNTERED SEVERE TURBULENCE FOR A PERIOD OF ABOUT 10 TO 20 SECONDS. THE AIRCRAFT DESCENDED 3500 FEET BEFORE THE FLIGHT CREW WAS ABLE TO REGAIN CONTROL OF THE AIRCRAFT'S DESCENT. THE FLIGHT THEN DIVERTED TO MEMPHIS, TENNESSEE IN ORDER TO OBGAIN MEDICAL ATTENTION FOR THOSE PERSONS INJURED IN THE CABIN SECTION OF THE AIRCRAFT.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

THE DELAYED INFLIGHT DECISION BY THE PILOT TO MANEUVER THE AIRCRAFT AWAY FROM THUNDERSTORM ACTIVITY.

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